1) Technical Field of the Invention
The present invention relates to a semiconductor device, and in particular, relates to the semiconductor device having a resin package formed by molding with thermoplastic resin, which reduces warpage of the resin package.
2) Description of Related Arts
Conventional power semiconductor devices such as a power module are, in general, categorized into two types of semiconductor devices. That is, one is a case-type semiconductor device having a case which is filled up with gel resin after a semiconductor chip is mounted on an insulating substrate in the case, and another one is a mold-type semiconductor device having a resin package which is molded with resin covering the semiconductor chip mounted on the insulating substrate. Also, the mold-type semiconductor device is further grouped into two of sub-groups, i.e., one formed by transfer-molding with thermosetting resin and another made by injection-molding with thermoplastic resin.
Unlike the case-type semiconductor device, the mold-type semiconductor device can eliminate manufacturing steps for securing the case on the insulating substrate and for filling in the case with gel resin, but it may have a problem that the resin package warps during hardening due to difference of linear thermal expansion coefficients between the resin package and various components such as the radiating plate and the semiconductor chip covered by the resin package. This may cause breakdown of the insulating substrate covered by the resin package, or may define a gap between the warped radiating plate and the external heat sink, thereby reducing radiation efficiency.
Among those mold-type semiconductor devices, a hybrid integrated circuit device formed by molding with thermoplastic resin is disclosed in a Japanese Patent Application, JPA 11-330317, having a patent family of a United Stated Patent, U.S. Pat. No. 6,259,157, which is incorporated herein by reference and referred to as “Reference 1”. Also, Reference 1 suggests that when injection-molding with the thermoplastic resin containing fiber glass, the direction of injection from a resin inlet is important, and also, in case where the resin package is elongated and has longer and shorter sides, in particular, the thermoplastic resin is to be injected from the resin inlet provided on the shorter side in the direction along the longer side so as to prevent the warpage of the resin package and the base plate. Thus, Reference 1 teaches that the thermoplastic resin mixed with fiber glass is injected in the direction along the longer side to orient the elongated fiber glass in the same longitudinal direction, thereby improving mechanical strength of the resin package along the longitudinal direction and reducing the warpage of the resin package.
In the meantime, a Japanese Patent Application, JPA 2003-318333, which is referred to as “Reference 2”, discloses another hybrid integrated circuit device formed by transfer-molding the thermosetting resin, in which the insulating resin package has grooves on the top surface thereof to avoid the warpage of the metal base plate. Reference 2 also teaches, as the reasons of the warpage, that the insulating resin is filled, hardened, and integrated with the base plate more quickly in the regions adjacent where the grooves are formed, and that the insulating resin close to the grooves has various angles to the mounting surface of the metal base plate.
However, in Reference 1, while the fiber glass of the resin package that is oriented in the longitudinal direction prevents the longitudinal warpage of the resin package, the linear expansion coefficient along the transverse direction perpendicular to the orienting direction of the fiber glass, which is substantially greater than one along the longitudinal direction, causes the warpage of the resin package and the base plate along the transverse direction. Therefore, Reference 1 cannot prevent, in the transverse direction, the breakdown of the insulating substrate and the reduction of radiation efficiency (due to the gap between the radiating plate and the external heat sink).
Also in Reference 2, the insulating resin filled and hardened more quickly adjacent the grooves is expected to improve stiffness encountering the stress that warps the resin package. However, in case that the thermoplastic resin is used, the cure temperature is lower and the cure time is longer than those when the thermosetting resin is utilized, therefore, the stiffness or mechanical strength of the transfer-molded resin package cannot be improved by forming the grooves on the insulating resin as Reference 2. It should be noted that Reference 2 describes nothing about the resin package formed by molding with the thermoplastic resin.
To address the aforementioned drawbacks, the present invention was made having one of purposes to provide a semiconductor device which can reduce the warpage of the resin package not only in the longitudinal direction but also transverse direction (the direction perpendicular to the orienting direction of the fiber glass).